Fuel injection apparatus and control method thereof

ABSTRACT

A fuel injection apparatus includes: a first obtaining unit that obtains a first index relating to an opening behavior of an injector; a second obtaining unit that obtains at least one of a second index relating to a maximum injection rate of the injector and a third index relating to an injection period; and a calculation unit that determines that injection hole corrosion has occurred in the injector when a first condition relating to the first index is established and at least one of a second condition relating to the second index and a third condition relating to the third index is established.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel injection apparatus and a control methodthereof.

2. Description of Related Art

In recent years, various measures to address aging variation in anopening/closing operation of a fuel injection valve (an injector) havebeen proposed. For example, in a fuel injection valve proposed inJapanese Patent Application Publication No. 2001-280189 (JP 2001-280189A), in order to address variation in an injection amount characteristiccaused by aging variation in a fuel injection valve that uses gas fuelor corrosive fuel, variation in an opening/closing delay of the fuelinjection valve is detected and a fuel injection pulse width iscorrected accordingly. In this fuel injection valve, an initially setinjection amount is maintained by correcting the fuel injection pulsewidth.

Incidentally, one cause of aging variation in the fuel injection valveis condensation of an acidic component of gas remaining in a cylinder.When the acidic component condenses and adheres to a tip end portion ofthe injector, an injection hole portion provided in the tip end portionof the injector may corrode. When the injection hole portion corrodes,atomization of the fuel injected from the ignition hole portion may beaffected, and as a result, smoke may be generated.

In the fuel injection valve disclosed in JP 2001-280189 A, however, theeffect of injection hole corrosion caused by condensed water is nottaken into consideration. More specifically, the injection hole startsto corrode by the condensed water from an injection hole outlet in thevicinity of a combustion chamber, and therefore substantially novariation is seen in the fuel injection amount. Hence, it is difficultto diagnose injection hole corrosion accurately simply by detecting theopening/closing delay.

SUMMARY OF THE INVENTION

An object of the invention is therefore to provide a fuel injectionapparatus and a control method thereof with which the presence in aninjector of injection hole corrosion caused by condensed water can bedetermined appropriately.

A fuel injection apparatus according to a first aspect of the inventionincludes: a first obtaining unit that obtains a first index relating toan opening behavior of an injector; a second obtaining unit that obtainsat least one of a second index relating to a maximum injection rate ofthe injector and a third index relating to an fuel injection period; anda calculation unit that determines that injection hole corrosion hasoccurred in the injector when a first condition relating to the firstindex is established and at least one of a second condition relating tothe second index and a third condition relating to the third index isestablished.

When injection hole corrosion occurs in the injector due to the adhesionof condensed water, a diameter of an outlet side of the injection holeincreases. In this case, the opening behavior of the injector does notdiffer greatly from that of a case in which injection hole corrosion hasnot occurred. On the other hand, variation is seen in at least one ofthe maximum injection rate and the injection period of the injector incomparison with a case in which injection hole corrosion has notoccurred, and therefore the presence of injection hole corrosion causedby condensed water adhesion is determined using a combination ofconditions relating to these indices.

Here, the first index relating to the opening behavior of the injectormay be at least one of a reduction amount and a reduction speed of afuel pressure immediately after the injector is opened. The first indexrelating to the opening behavior of the injector may also be at leastone of a needle speed and a needle lift immediately after the injectoris opened.

In the first aspect described above, the calculation unit may calculatea parameter on which to evaluate an injection hole corrosion amount inthe injector on the basis of at least one of the second index and thethird index, and correct the fuel pressure of the injector on the basisof the parameter. Further, the calculation unit may determine acorrection amount to be applied to the fuel pressure on the basis of asmoke amount increase. When injection hole corrosion caused by condensedwater adhesion occurs, substantially no variation occurs in a fuelinjection amount per injection, and therefore an air-fuel ratio remainsunchanged while a smoke characteristic deteriorates. Accordingly, thefuel pressure (an injection pressure) is varied so that thedeterioration of the smoke characteristic can be offset. As a result,adverse effects caused by deterioration of the smoke characteristic,such as a filter blockage, for example, can be avoided.

A control method for a fuel injection apparatus according to a secondaspect of the invention includes: obtaining a first index relating to anopening behavior of an injector; obtaining at least one of a secondindex relating to a maximum injection rate of the injector and a thirdindex relating to an injection period; and determining that injectionhole corrosion has occurred in the injector when a first conditionrelating to the first index is established and at least one of a secondcondition relating to the second index and a third condition relating tothe third index is established.

With the fuel injection apparatus according to the first aspect of theinvention and the control method for a fuel injection apparatusaccording to the second aspect of the invention, the presence in theinjector of injection hole corrosion caused by condensed water can bedetermined appropriately.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a schematic illustrative view showing a configuration of anengine incorporated with a fuel injection apparatus according to a firstembodiment;

FIG. 2 is a schematic illustrative view showing a configuration of aninjector;

FIG. 3A is a schematic illustrative view showing a shape of an injectionhole when injection hole corrosion has not occurred, and FIG. 3B is aschematic illustrative view showing the shape of the injection hole wheninjection hole corrosion has occurred;

FIG. 4 is a flowchart showing an example of control of the fuelinjection apparatus;

FIG. 5 is a flowchart showing another example of control of the fuelinjection apparatus;

FIG. 6 is a flowchart showing a further example of control of the fuelinjection apparatus;

FIG. 7 is an illustrative view showing a first index, a second index,and a third index;

FIG. 8 is an illustrative view showing an example of a measurementresult of a fuel inlet pressure waveform;

FIG. 9 is an illustrative view showing differences in a needle liftaccording to the presence or absence of deposit accumulation;

FIG. 10 is an illustrative view illustrating an effect of an injectionhole flow rate;

FIGS. 11A and 11B are a flowchart showing an example of actionsimplemented when injection hole corrosion is detected;

FIG. 12 is a graph showing an example of a relationship between aninjection hole corrosion amount and a maximum injection rate;

FIG. 13 is a graph showing an example of a relationship between theinjection hole corrosion amount, an injection pressure, and a smokegeneration amount;

FIG. 14 is a block diagram showing a part of a fuel injection apparatusaccording to a second embodiment;

FIG. 15 is an illustrative view showing an example of variation in aneedle speed and a needle lift; and

FIG. 16 is an illustrative view showing variation in the maximuminjection rate.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will be described below with reference tothe attached drawings. Note, however, that dimensions of respectiveparts, ratios, and so on illustrated in the drawings may not matchactual dimensions, ratios, and so on perfectly. Further, in certaindrawings, detailed parts may be omitted.

(First Embodiment) FIG. 1 is a schematic illustrative view showing aconfiguration of an engine 100 incorporated with a fuel injectionapparatus 1 according to this embodiment. FIG. 2 is a schematicillustrative view showing a configuration of an injector 107.

The engine 100 is an engine that performs in-cylinder injection, or morespecifically a diesel engine. The engine 100 has four cylinders. Theengine 100 includes an engine main body 101, and first to fourthcylinders are provided in the engine main body 101. The fuel injectionapparatus 1 is incorporated into the engine 100. The fuel injectionapparatus 1 includes first to fourth injectors 107-1 to 107-4corresponding respectively to the first to fourth cylinders. Morespecifically, the first injector 107-1 is attached to the firstcylinder, and a second injector 107-2 is attached to a second cylinder.A third injector 107-3 is attached to a third cylinder, and the fourthinjector 107-4 is attached to the fourth cylinder. The first to fourthinjectors 107-1 to 107-4 are respectively connected to a common rail120, and high pressure fuel is supplied thereto from the common rail120.

The engine 100 includes an intake manifold 102 and an exhaust manifold103 attached to the engine main body 101. An intake pipe 104 isconnected to the intake manifold 102. An exhaust pipe 105 and one end ofan exhaust gas recirculation (EGR) passage 108 are connected to theexhaust manifold 103. Another end of the EGR passage 108 is connected tothe intake pipe 104. An EGR cooler 109 is provided in the EGR passage108. Further, an EGR valve 110 is provided in the EGR passage 108 tocontrol a flow of exhaust gas. An air flow meter 106 is connected to theintake pipe 104. The air flow meter 106 is electrically connected to anelectronic control unit (ECU) 111. An injector 107-i (where i is acylinder number), or more specifically the first to fourth injectors107-1 to 107-4, is electrically connected to the ECU 111. The ECU 111issues engine stop fuel injection demands individually to the first tofourth injectors 107-1 to 107-4.

An NE sensor 112 that measures an engine rotation speed, a watertemperature sensor 113 that measures a water temperature of coolingwater, and a fuel temperature sensor 114 that measures a fueltemperature are electrically connected to the ECU 111. The ECU 111performs various types of control around the engine.

Referring to FIG. 2, a nozzle body 107 a is provided on a tip endportion of the injector 107. An injection hole 107 a 1 is provided inthe nozzle body 107 a. FIGS. 3A and 3B show a shape of the injectionhole 107 a 1 schematically. More specifically, FIG. 3A is a schematicillustrative view showing the shape of the injection hole 107 a 1 wheninjection hole corrosion has not occurred, and FIG. 3B is a schematicillustrative view showing the shape of the injection hole 107 a 1 wheninjection hole corrosion has occurred. A needle valve is housed in aninterior of the injector 107 to be free to slide. When condensed wateradheres to the nozzle body 107 a on the tip end portion of the injector107, a diameter of an outlet side of the injection hole 107 a 1increases, as shown in FIG. 3B. A corrosion effect on an inlet side, onthe other hand, is small, and therefore a diameter of the inlet side isunlikely to vary. In other words, a feature of injection hole corrosioncaused by the adhesion of condensed water is an increase in the diameterof the outlet side, which is exposed to an interior of a combustionchamber. Note that plating processing may be implemented on theinjection hole 107 a 1. In this case, the injection hole corrosionincludes peeling of the plating applied to the injection hole 107 a 1.

Referring to FIG. 2, a high pressure fuel portion 107 b is provided on abase end side of the injector 107 to supply fuel into the interior ofthe injector 107. The high pressure fuel portion 107 b is connected tothe common rail 120, and a pressure gauge 115 that measures a fuel inletpressure Pcr of the injector 107 is provided on a connection pathbetween the high pressure fuel portion 107 b and the common rail 120.The pressure gauge 115 measures a pressure (a fuel pressure) of injectedfuel supplied from the common rail 120 to the injector 107. The fuelinlet pressure Pcr varies according to a fuel injection operation of theinjector 107. The pressure gauge 115 is electrically connected to theECU 111. The ECU 111 and the pressure gauge 115 are included in firstobtaining unit that obtains a first index relating to an openingbehavior of the injector 107 and second obtaining unit that obtains asecond index relating to a maximum injection amount of the injector 107and a third index relating to an injection period of the injector 107.The ECU 111 also functions as a calculation unit. The first index,second index, and third index will be described in detail below.

An example of control of the fuel injection apparatus 1 will now bedescribed with reference to FIGS. 4 to 8. FIG. 4 is a flowchart showingan example of control of the fuel injection apparatus 1. FIG. 7 is anillustrative view showing the first index, the second index, and thethird index. FIG. 8 is an illustrative view showing an example of ameasurement result of a fuel inlet pressure waveform. FIG. 9 is anillustrative view showing differences in a needle lift according to thepresence or absence of deposit accumulation. FIG. 10 is an illustrativeview illustrating an effect of an injection hole flow rate.

Before describing specific control, the first to third indices will bedescribed with reference to FIG. 7. The first index is indicated by (1)Opening behavior a in FIG. 7. The second index is indicated by (2)Maximum injection rate dQmax in FIG. 7. The third index is indicated by(3) Injection period tinj in FIG. 7. All of these indices can be learnedfrom variation in the fuel inlet pressure Pcr. Among conditions relatingto the indices, a first condition relating to the first index must beestablished in order to determine that injection hole corrosion hasoccurred in the injector. Further, injection hole corrosion isdetermined to have occurred in the injector when at least one of asecond condition relating to the second index and a third conditionrelating to the third index is established in addition to the firstcondition. Naturally it may also be determined that injection holecorrosion has occurred when all of the conditions are established.

Here, the first index may be set as at least one of a reduction amountand a reduction speed of the fuel pressure immediately after theinjector 107 is opened. More specifically, the first index may be set asa reduction amount and a reduction speed of the fuel inlet pressure Pcrimmediately after the injector 107 is opened. Accordingly, the conditionrelating to the first index may be set to be established when an amountof variation in the first index is equal to or smaller than apredetermined value. A needle of the injector 107 is lifted by a balancebetween a pressure in a suction chamber provided in the nozzle body 107a 1 and a pressure in a control chamber provided on the base end side ofthe injector 107. Therefore, when no variation occurs in a relationshipbetween the pressure in the suction chamber and the pressure in thecontrol chamber, no variation is seen in the opening behavior a. Here,focusing on behavior occurring when the injector 107 is open, a flowcoefficient in an initial injection stage is reduced by roughening of aninner surface of the injection hole, and therefore the pressure in thesuction chamber does not decrease. Hence, even when injection holecorrosion occurs, variation in the behavior of the injector immediatelyafter opening is very small. In other words, the amount of variation inthe first index remains at or below the predetermined value. A conditionin which the amount of variation in the first index remains at or belowthe predetermined value is a characteristic phenomenon observed wheninjection hole corrosion caused by the adhesion of condensed wateroccurs, and therefore this condition is a requirement for determiningthe presence of injection hole corrosion. Note that when the reductionamount or the reduction speed of the fuel inlet pressure Pcr immediatelyafter opening is employed as the first index, as described above, aperiod serving as “immediately after opening” may be set as desired. Inother words, the period “immediately after opening” may be setappropriately in consideration of specifications, characteristics, andindividual differences in the injector 107. In FIGS. 7 and 8, forexample, a period extending from opening (a start time) to a time (anend time) at which the fuel inlet pressure Pcr decreases by a maximumamount can be set as the period immediately after opening.

Differences a case in which the injection hole diameter varies (e.g.,decreases) over an entire region of the injection hole and a case inwhich the injection hole diameter varies only at the outlet side willnow be described with reference to FIGS. 9 and 10. Deposits typicallyaccumulate over the entire region of the injection hole, and therefore,when deposits accumulate, the diameter of the injection hole varies overan entire lengthwise direction region. In other words, the injectionhole corrodes in a different manner to a case in which the injectionhole corrosion is caused by condensed water adhesion, in which only thediameter of the injection hole outlet side varies. When depositsaccumulate, it becomes more difficult to inject the fuel, and therefore,in comparison with a case in which no deposits have accumulated, thepressure in the suction chamber increases from the initial injectionstage. As a result, as shown in FIG. 7, a needle lift speed increases,and since the pressure in the suction chamber remains high, the needlelift also increases, leading to an increase in an open period (theinjection period).

When the actual effect of the injection hole flow rate is evaluatedusing injectors having different injection hole diameters in order tocompare opening behaviors according to the presence or absence ofdeposit accumulation, results shown in FIG. 10 are obtained. It isevident from FIG. 10 that when the injection hole flow rate increases,the injection amount of the injector also increases. Therefore, when thediameter varies (e.g., decreases) over the entire region of theinjection hole, a difference in an initial injection rate is detected.When only the diameter of the injection hole at the outlet side varies(e.g., decreases) due to injection hole corrosion, on the other hand, nodifference occurs in the opening behavior. Hence, in the fuel injectionapparatus 1 according to this embodiment, the first condition relatingto whether or not the amount of variation in the first index remains ator below the predetermined value is a requirement for determining thatinjection hole corrosion has occurred.

The second index relates to variation in the maximum injection ratedQmax. An injection rate dQ is calculated using following Equation (1).

dQ=Cd×A×√(2×ΔP/ρ)   Equation 1

Here, Cd is the flow coefficient, A is an injection hole outlet surfacearea, ΔP is a difference in pressure between a pressure inside of thesuction chamber pressure and a pressure outside of an injector hole, andρ is a fuel density.

Hence, when the injection hole outlet surface area increases, theinjection rate dQ also increases. Variation in the injection rate dQ isa phenomenon observed when injection hole corrosion occurs, and cantherefore be set as an index for determining the presence of injectionhole corrosion. Note that an increase in the injection rate dQ may alsobe learned as a reduction in the fuel inlet pressure Pcr. Further, amomentary injection rate dQ obtained at a desired timing may be employedas the maximum injection rate dQmax. As shown in FIG. 7, for example,the injection rate dQ at a timing where the fuel inlet pressure Pcrbecomes substantially constant may be employed.

The third index relates to variation in the injection period tinj. Evenwhen injection hole corrosion occurs, the fuel injection amount per oneinjection does not vary. Therefore, when the maximum injection ratedQmax increases, the injection period tinj is shortened. Accordingly,the injection period tinj may also be used as an index for determiningthe presence of injection hole corrosion. The phenomenon whereby theinjection period tinj shortens when injection hole corrosion occurs canalso be explained by an increase in an opening speed of the needlevalve, which occurs when the pressure in the suction chamber decreasesearly due to an increase in the maximum injection rate dQmax.

When either one of the second condition relating to the second index andthe third condition relating to the third index is satisfied togetherwith the first condition, it may be determined that injection holecorrosion has occurred.

An example of control based on determinations of the three conditionsdescribed above will now be described using a flowchart shown in FIG. 4.Note that in this embodiment, as described above, the conditions aredetermined on the basis of variation in the fuel inlet pressure Pcr,which is measured by the pressure gauge 115.

First, in step S1, a determination is made as to whether or not aninjection hole corrosion determination injection condition is satisfied.To determine whether or not injection hole corrosion has occurred, eachindex is compared with a corresponding reference value. Here, indicesset at the time of factory shipping, for example, may be employed as thereference values. In other words, the indices are compared respectivelywith so-called normal condition values obtained when injection holecorrosion has not occurred. The injection hole corrosion determinationinjection condition is aligned with a reference value obtainingcondition. This condition may be set as desired, but by setting a regionin which the injection amount is comparatively large, such as a timingof a medium/high injection pressure, for example, differences are morelikely to appear, increasing accuracy of the injection hole corrosiondetermination.

When the determination of step S1 is negative, the processing returns.When the determination of step S1 is affirmative, the processingadvances to step S2. In step S2, a waveform of the fuel inlet pressurePcr is obtained. Next, in step S3, the injection hole corrosiondetermination indices (the first to third indices) are detected. Inother words, the fuel inlet pressure waveform shown in FIG. 6 isobtained.

In step S4 following step S3, a determination is made as to whether ornot an opening behavior condition serving as the first index, or inother words the first condition relating to the first index, issatisfied. More specifically, the fuel inlet pressure Pcr in the openperiod during when the injection hole is open is compared with areference fuel inlet pressure Pcr, and a determination is made as towhether or not an amount of variation in the fuel inlet pressure Pcr isequal to or smaller than a predetermined value. When the determinationof step S4 is negative, the processing advances to step S7, where it isdetermined that injection hole corrosion has not occurred. Theprocessing is then returned. When the determination of step S4 isaffirmative, on the other hand, the processing advances to step S5. Instep S5, a determination is made as to whether or not a conditionrelating to the maximum injection rate dQmax serving as the secondindex, or in other words the second condition relating to the secondindex, is satisfied. More specifically, the maximum injection rate dQmaxis compared with a reference dQmax to determine whether or not themaximum injection rate dQmax has increased. Note that when dQmaxincreases, the fuel inlet pressure Pcr falls below the reference fuelinlet pressure Pcr. When the determination of step S5 is affirmative,the processing advances to step S8, where it is determined thatinjection hole corrosion has occurred. The processing is then returned.In other words, injection hole corrosion is determined to have occurredwhen both the first condition and the second condition are satisfied.

When the determination of step S5 is negative, on the other hand, theprocessing advances to step S6. In step S6, a determination is made asto whether or not a condition relating to the fuel injection period tinjserving as the third index, or in other words the third conditionrelating to the third index, is satisfied. More specifically, the fuelinjection period tinj is compared with a reference injection period tinjto determine whether or not the fuel injection period tinj has becomeshorter. When the determination of step S6 is affirmative, theprocessing advances to step S8, where it is determined that injectionhole corrosion has occurred. The processing is then returned. In otherwords, injection hole corrosion is determined to have occurred when boththe first condition and the third condition are satisfied. When thedetermination of step S6 is negative, on the other hand, or in otherwords when neither the second condition nor the third condition issatisfied, the processing advances to step S7, where it is determinedthat injection hole corrosion has not occurred. The processing is thenreturned.

Note that the order in which the processing of step S5 and step S6 isperformed may be reversed. Moreover, as long as the first to thirdconditions can ultimately be determined, there are no limitations on theorder in which the processing of step S4 to step S6 is performed.Furthermore, the processing may be returned when the second condition orthe third condition is satisfied together with the first condition, orinjection hole corrosion may be determined to have occurred when all ofthe conditions are satisfied.

Further, as shown in FIG. 5, the processing of step S6 in FIG. 4 may beomitted. More specifically, when the determination of step S5 isnegative, the processing advances to step S7, where it is determinedthat injection hole corrosion has not occurred, and then the processingis returned. When the determination of step S5 is affirmative,meanwhile, the processing advances to step S8, where it is determinedthat injection hole corrosion has occurred, and then the processing isreturned. In other words, injection hole corrosion is determined to haveoccurred when the condition relating to the maximum injection rate dQmaxserving as the second index is satisfied in addition to the openingbehavior condition serving as the first index. Furthermore, according toa modified example shown in FIG. 6, the processing of step S5 in FIG. 4may be omitted. More specifically, when the determination of step S6 isnegative, the processing advances to step S7, where it is determinedthat injection hole corrosion has not occurred, and then the processingis returned. When the determination of step S6 is affirmative,meanwhile, the processing advances to step S8, where it is determinedthat injection hole corrosion has occurred, and then the processing isreturned. In other words, injection hole corrosion is determined to haveoccurred when the condition relating to the injection period serving asthe third index is satisfied in addition to the opening behaviorcondition serving as the first index.

With the fuel injection apparatus 1 according to this embodiment, asdescribed above, the presence of injection hole corrosion caused bycondensed water in the injector can be determined appropriately.

Next, referring to FIGS. 11 to 13, countermeasures taken when injectionhole corrosion is confirmed will be described. In consideration of thefact that when injection hole corrosion occurs, a smoke characteristicdeteriorates, the purpose of the countermeasures is to implement actionsto offset the deterioration of the smoke characteristic. In thisembodiment, the injection pressure (the fuel pressure) is corrected.

Referring to FIGS. 11A and 11B, in step S21, a determination is made asto whether or not injection hole corrosion has occurred. Morespecifically, a determination is made as to whether or not the injectionhole corrosion determination has been performed in step S8 of theflowchart shown in FIGS. 4, 5 and 6. The processing of step S21 isrepeated until the determination becomes affirmative. When thedetermination of step S21 is affirmative, the processing advances tostep S22. In step S22, the waveform of the fuel inlet pressure Pcr isobtained again. The waveform obtained in step S2 can be used as thiswaveform. In step S23 following step S22, the injection hole corrosionamount determination indices are detected from the obtained waveform.More specifically, the maximum injection rate dQmax serving as thesecond index and the fuel injection period tinj serving as the thirdindex are detected. In this embodiment, an injection hole corrosionamount Δd serving as a parameter on which to evaluate the injection holecorrosion amount is calculated on the basis of the second index and thethird index. In this embodiment, the injection hole corrosion amount Δditself is calculated, but a value having a correlation with theinjection hole corrosion amount Δd may be used as the parameter on whichto evaluate the injection hole corrosion amount. Note that either one ofthe second index and the third index may be used as the injection holecorrosion amount determination index, and the parameter on which toevaluate the injection hole corrosion amount may be calculated on thebasis of the used index.

In step S24 following step S23, an injection hole corrosion amountΔd_(dQ) based on the maximum injection rate dQmax is calculated. Theinjection hole corrosion amount Δd_(dQ) can be calculated from f(dQmaxi, dQmax0). More specifically, the injection hole corrosion amountΔd_(dQ) can be determined from a difference between dQmaxi and dQmax0.Here, the suffix i denotes a measurement value obtained in step S22, andthe suffix 0 denotes a reference value serving as a comparison subject.This applies likewise to suffixes used in the following description.

In step S25 following step S24, an injection hole corrosion amountΔd_(ti) based on the injection period tinj is calculated. The injectionhole corrosion amount Δd_(ti) can be calculated from f (tinji, tinj0).More specifically, the injection hole corrosion amount Δd_(ti) can bedetermined from a difference between tinji and tinj0.

Note that there are no limitations on the order in which step S24 andstep S25 are performed. In other words, the order in which the two stepsare performed may be reversed, or the two steps may be performedsimultaneously in parallel.

In step S26 following step S25, a determination is made as to whetherΔd_(dQ) or Δd_(ti) is larger. When the determination is affirmative, orin other words when Δd_(dQ) is determined to be larger, the processingadvances to step S27, where Δd_(dQ) is employed as the injection holecorrosion amount Δd. When, on the other hand, the determination isnegative, or in other words when Δd_(ti) is determined to be larger, theprocessing advances to step S28, where Δd_(ti) is employed as theinjection hole corrosion amount Δd. By employing the larger numericalvalue as Δd in this manner, the determination can be made more safely.In this embodiment, the two values are compared and the larger value isemployed, but instead, an average value of the two values may beemployed as the injection hole corrosion amount Δd.

In step S29 following step S27 or step S28, a fuel pressure correctionvalue ΔPcr is calculated on the basis of the injection hole corrosionamount Δd. ΔPcr is calculated from f (Δd, ΔPcr). Here, referring to FIG.13, it is evident that when a corrosion time increases, leading to anincrease in the injection hole corrosion amount, the maximum injectionrate dQmax likewise tends to increase. Typically, an increase in themaximum injection rate dQmax leads to an increase in a smoke generationamount. Referring to FIG. 13, it is evident that when the fuel pressureremains constant, the smoke generation amount increases as injectionhole corrosion advances, or in other words as the injection holecorrosion amount increases. This tendency appears more strikingly towarda region in which the fuel inlet pressure Pcr, or in other words theinjection pressure (the fuel pressure) is low. For example, if a userwishes to set an equivalent smoke generation amount to an amount ofsmoke generated when fuel is injected at an injection pressure a1 whilethe injector 107 is still new such that injection hole corrosion has notyet occurred, the fuel must be injected at an injection pressure a2 in acase where the injection hole corrosion amount is indicated to be smallin FIG. 13. Similarly, in a case where the injection hole corrosionamount is indicated to be large in FIG. 13, the fuel must be injected atan injection pressure a3. Hence, in step S29, the fuel pressure (theinjection pressure) is varied such that the deterioration of the smokecharacteristic can be offset. Referring to FIGS. 11A and 11B, an amountby which the fuel pressure is corrected can be determined in accordancewith a smoke amount increase. When injection hole corrosion occurs, novariation is seen in the fuel injection amount, and therefore anair-fuel ratio does not vary either. Hence, the fuel pressure iscorrected so as to be able to offset the smoke amount increase.

In step S30 following step S29, a determination is made as to whether ornot the injection hole corrosion amount equals or exceeds a thresholdΔdmax of the injection hole corrosion amount Δd. Here, the thresholdΔdmax is set at a value at which it may be impossible to avoid a problemthat cannot easily be dealt with in the fuel injection apparatus 1, suchas a filter blockage, even by increasing the fuel pressure. When thedetermination of step S30 is affirmative, the processing advances tostep S31, where an MIL is lit. As a result, a user is prompted toimplement an action such as taking the vehicle to a repair shop. Whenthe determination of step S30 is negative, on the other hand, injectionpressure correction is executed on the basis of the correction amountcalculated in step S29. As a result, the increase in the smokegeneration amount caused by the deterioration of the smokecharacteristic can be counteracted. Following steps S31 and S32, theprocessing is returned.

Note that in addition to the action of step S32, an injection holecorrosion countermeasure may be implemented. For example, a post-enginestoppage fuel injection may be performed to counteract the injectionhole corrosion. When plating processing has been implemented on theinjector 107 and the plating has peeled away, an action such asperforming a post-engine stoppage fuel injection is effective. In otherwords, progression of the corrosion that occurs when the plating peelsaway can be delayed. A determination as to whether or not the platinghas peeled away can be made similarly to estimation of the injectionhole corrosion amount. Further, either an identical value to thethreshold Δdmax shown in the flowchart of FIGS. 11A and 11B or adifferent value may be employed as a threshold for determining whetheror not to implement the injection hole corrosion countermeasure.Moreover, the injection hole corrosion countermeasure may be implementedindependently regardless of whether or not injection pressure correctionis executed.

(Second Embodiment) Next, a second embodiment will be described withreference to FIGS. 14 to 16. In the first embodiment, the waveform ofthe fuel inlet pressure Pcr is obtained in order to obtain the first tothird indices. In the second embodiment, on the other hand, as shown inFIG. 14, the various indices are obtained by analyzing a needle behaviorusing a needle lift sensor 120 that is electrically connected to the ECU111. More specifically, a needle speed and a needle lift immediatelyafter opening of the injector 107 is employed as the first indexrelating to the opening behavior of the injector 107.

FIG. 15 shows aging variation in the needle speed and the needle lift.It can be seen that the needle lift and the needle speed within a periodimmediately after opening, which is set as desired in a similar mannerto the first embodiment, differ depending on whether or not injectionhole corrosion has occurred. In other words, it can be seen that thefirst condition relating to the first index is satisfied. Further,focusing on the needle speed immediately before closing, the needlespeed when injection hole corrosion has occurred is higher than theneedle speed when injection hole corrosion has not occurred, andtherefore the fuel injection period tinj is shorter. In other words, itcan be seen that the third condition relating to the third index issatisfied. Variation in the maximum injection rate, shown in FIG. 16,can be calculated from the variation in the needle lift and needle speedshown in FIG. 15, and it is evident from FIG. 16 that the maximuminjection rate dQmax has increased. In other words, it can be seen thatthe second condition relating to the second index is also satisfied.

Hence, the various indices can also be obtained on the basis of thebehavior of the needle provided in the injector 107, whereupon thepresence of injection hole corrosion can be determined on the basis ofthe obtained indices.

The embodiments described above are merely examples of implementation ofthe invention, and the invention is, not limited thereto. As is evidentfrom the above description, various amendments may be made to theembodiments within the scope of the invention, and moreover, variousother embodiments are included within the scope of the invention.

1. A fuel injection apparatus comprising: a first obtaining unit thatobtains a first index relating to an opening behavior of an injector; asecond obtaining unit that obtains at least one of a second indexrelating to a maximum injection rate of the injector and a third indexrelating to an fuel injection period; and a calculation unit thatdetermines that injection hole corrosion has occurred in the injectorwhen a first condition relating to the first index is established and atleast one of a second condition relating to the second index and a thirdcondition relating to the third index is established wherein the firstcondition is established when an amount of variation in the first indexis equal to or smaller than a predetermined value, and the secondcondition is established when the second index increases relative to areference value, and the third condition is established when the thirdindex shortens relative to a reference value.
 2. The fuel injectionapparatus according to claim 1, wherein the first index relating to theopening behavior of the injector is at least one of a reduction amountand a reduction speed of a fuel pressure immediately after the injectoris opened.
 3. The fuel injection apparatus according to claim 1, whereinthe first index relating to the opening behavior of the injector is atleast one of a needle speed and a needle lift immediately after theinjector is opened.
 4. The fuel injection apparatus according to claim1, wherein the calculation unit calculates a parameter on which toevaluate an injection hole corrosion amount in the injector on the basisof at least one of the second index and the third index, and correctsthe fuel pressure of the injector on the basis of the parameter.
 5. Thefuel injection apparatus according to claim 4, wherein the calculationunit determines a correction amount to be applied to the fuel pressureon the basis of a smoke amount increase.
 6. The fuel injection apparatusaccording to claim 1, wherein the second index is the maximum injectionrate of the injector.
 7. (canceled)
 8. The fuel injection apparatusaccording to claim 1, wherein the third index is the fuel injectionperiod of the injector.
 9. (canceled)
 10. A control method for a fuelinjection apparatus, comprising: obtaining a first index relating to anopening behavior of an injector; obtaining at least one of a secondindex relating to a maximum injection rate of the injector and a thirdindex relating to an fuel injection period; and determining thatinjection hole corrosion has occurred in the injector when a firstcondition relating to the first index is established and at least one ofa second condition relating to the second index and a third conditionrelating to the third index is established, wherein the first conditionis established when an amount of variation in the first index is equalto or smaller than a predetermined value, and the second condition isestablished when the second index increases relative to a referencevalue, and the third condition is established when the third indexshortens relative to a reference value.